Direct emitter coupled transistor amplifiers, with bias currents and gain controlled by a constant current source connected to the common emitter terminal, have been known before in the state of the art and are widely used in integrated circuits. Such amplifiers are noted for their large signal handling capabilities and their stable gain and bias level characteristics. Amplifiers of this type, however, have limited absolute values of noise figure and gain, due to the resistance and noise properties of the constant current source. Emitter coupled amplifiers also have a poor high frequency response due to the Miller capacitance effect, and are not economical in their use of current.
A transistor cascode stage, defined as a common emitter stage amplifier with its output directly connected to the input of a common base stage amplifier, is certainly well known in the state of the art. Cascode stages possess good high frequency response, low noise figure characteristics, and are economical in their use of current. However, cascode stages do not have large signal capabilities; and if biased by a constant current source, cascode stages possess stable gain characteristics, only if the input signal is small enough so that the operation of the constant current source is not materially disrupted.
A cascode stage has been combined with an emitter coupled transistor before, but only where the emitter coupled transistor has been connected to the output device of the cascode stage. The emitter coupled transistor is used as an AGC cntrol and preserves the current economy of a cascode configuration, but does not increase the signal handling capabilities of the cascode amplifier.
Connecting amplifiers in cascade is common and obtains the multiplication of the gain of individual amplifiers while permitting a direct coupled connection of the amplifiers. Cascade connections result in each amplifier drawing a separate current and therefore are not economical in their use of current. Cascode connection of amplifiers is also an old technique which is economical in current drain, but does not permit a direct coupling of individual stages. Cascode stacking of amplifiers also requires a higher value of voltage potential than an equivalent cascade connection of amplifiers.